1. Field of the Invention
Embodiments of the present invention relate to biomedical sensor technology and, in particular, to implantable, multi-parameter sensing systems and methods.
2. Description of Related Art
Continuous parameter measurement is important in the detection and monitoring of disease in patients. The ability to monitor biological or physiological parameters, analytes and other parameters in a patient in emergency rooms, intensive care units and other hospital settings is critical in stabilizing patients and reducing mortality rates. The monitoring of blood oxygen saturation, blood pressure, glucose, lactate, temperature, ion concentration, such as potassium, for example, and pH, for example, provides an indication of the state of tissue oxygen balance in the patient, knowledge of which is crucial in preventing a patient from progressing toward a serious, debilitating medical condition or even death.
Various situations require prompt monitoring and response to a change in body chemistry or other patient parameters. For example, sepsis, a toxic condition resulting from the spread of bacteria or their products from a focus of infection, can lead to global tissue hypoxia, multiple organ failures, cardiovascular collapse and eventual death. Increased blood lactate concentrations and decreased mixed venous oxygen saturation are classic indicators of the early phases of septic shock. By monitoring these parameters, blood chemistry levels can be regulated and the incidence of sepsis decreased.
The prevention of sepsis is becoming increasingly important. Cases of sepsis occur more frequently in elderly persons than in younger populations. As the number of elderly persons nationwide and worldwide continues to increase, the number of cases of sepsis can be expected to increase as well.
Blood glucose is another parameter that requires monitoring in a medical setting in order to reduce injury and mortality rates. For example, for patients who are in an intensive care environment, especially those with diabetes, glucose monitoring is critical. If the amount of glucose in the diabetic patient's system is not maintained at proper levels, the patient may sustain serious or life-threatening injury. If too much glucose accumulates in the diabetic patient's system, the patient could become hyperglycemic, resulting in shortness of breath, nausea and vomiting at best or diabetic coma and death in the worst case. If there is too little glucose in the diabetic patient's system, the patient could become hypoglycemic, resulting in dizziness, sweating and headache at best and unconsciousness and death in the worst case.
Electrolyte and ion monitoring may have great potential for some electrolyte disorders. For example, low sodium or hyponatremia (an acute or chronic condition caused by kidney failure, pneumonia, meningitis, trauma, adrenal/pituitary gland insufficiency, congestive heart failure and cirrhosis) can cause water from the body fluids to move into the higher osmolarity tissue, causing the tissue to expand (edema). One clinical manifestation of this syndrome is increased brain pressure from cerebral edema. Potassium deficit (<3.5 mmol/L) has been linked with increased incidence of stroke in elderly individuals, especially those with arterial fibrillation. Additionally, serum potassium level has been a predictor of serious peri- and intra-operative arrhythmia, and postoperative arterial fibrillation.
Traditionally, the monitoring of patient parameters in a hospital or other medical setting has been accomplished by drawing a blood sample and sending the sample to a laboratory for analysis. This type of monitoring process, while well-established and providing accurate results, is time-consuming and, indeed, time-prohibitive in an emergency situation. By the time lab results return to an attending physician, the patient may have already entered into a serious state or even may have already died.
Some industry attempts have been made to provide continuous, immediate monitoring of patient parameters. For example, Diametrics Medical, Inc., has developed several sensing systems for monitoring patient parameters, such as the NEUROTREND Sensor and the PARATREND7+ Sensors. The NEUROTREND Sensor is a disposable, single-use device for the continuous measurement of intra cranial pH, pCO2, pO2, and temperature that is used in conjunction with an appropriate intracranial access device. The device incorporates optical sensors and thermocouples for the measurement of pH, pCO2, and pO2, and a thermocouple for temperature measurement. The NEUROTREND sensor indicates the perfusion and metabolic acidosis/alkalosis status of cerebral tissue in the vicinity of the sensor. The PARATREND7+ Sensors are disposable, single-use fiber optic devices for continuous measurement of pH, pCO2, pO2 and temperature, providing real-time oxygenation, ventilation and metabolic information for critically ill patients.
However, the NEUROTREND Sensors and the PARATREND7+ Sensors have limited capabilities. Optical sensors lose effectiveness quickly when proteins deposit on their surface, which is inevitable in the body. The NEUROTREND Sensors and the PARATREND7+ Sensors, which are based on optical sensors, thus, tend to lose their effectiveness quickly. Accordingly, medical professionals must still use conventional techniques for obtaining reliable, quantifiable parameter values in addition to the values indicated by the NEUROTREND Sensors and the PARATREND7+ Sensors when administering to patients.
To date, there have been no implantable sensors providing continuous, quantifiable, simultaneous measurement values for patient parameters. In particular, there have been no implantable sensors providing continuous, quantifiable, simultaneous measurement values for lactate, glucose, pH, temperature, venous oxygen pressure, venous oxygen concentration and potassium. An implantable, multi-parameter sensor that monitors one or more of glucose, lactate, pH, temperature, venous oxygen pressure, venous oxygen concentration and blood potassium could be used advantageously in hospital or medical settings, in critical care, emergency care and intensive care situations, in triage, surgery and in field applications. For example, because a patient's blood glucose concentration may increase during kidney dialysis, the monitoring of glucose, oxygen and temperature during dialysis may be helpful.